1. Field of the Invention
The present invention relates to a piezoelectric thin film vibrator having a piezoelectric device formed by using thin film formation technology, a fabrication method thereof, a driving apparatus and a piezoelectric motor using the same.
2. Description of the Related Art
A piezoelectric vibrator utilizing the piezoelectric effect of a piezoelectric device is used in an ultrasonic motor (piezoelectric motor), a piezoelectric actuator, etc. Generally, the piezoelectric device has a pair of electrodes and a piezoelectric product sandwiched between the electrodes. For example, for the piezoelectric product, a piezoelectric ceramic is used.
However, the piezoelectric device using the piezoelectric ceramic has a problem that the volume and the film thickness thereof are increased. When the volume and the film thickness of the piezoelectric product are increased, high drive voltage needs to be applied in order to obtain sufficient power out of the piezoelectric device. When high drive voltage is applied, the piezoelectric device tends to break. Furthermore, piezoelectric ceramic powder is separated from the piezoelectric ceramic, and it easily falls off. Thus, a problem arises that the fallen piezoelectric ceramic powder damages the piezoelectric vibrator to cause frequent failure.
For a method of solving the problems above, thin film formation technology is known in which a piezoelectric product is formed by using a vapor deposition apparatus, a sputtering apparatus, or a CVD apparatus. A piezoelectric thin film is used for the piezoelectric product to reduce the device thickness. Thus, the applied voltage can be made small, and the overall size of the piezoelectric device can be made small.
A piezoelectric thin film vibrator using the piezoelectric thin film has a resonator which generates flexure traveling waves and is formed of a silicon substrate, for example, a lower electrode which is formed on the resonator, a piezoelectric thin film which is formed on the lower electrode, and an upper electrode which is formed on the piezoelectric thin film. A predetermined alternating voltage is applied to the piezoelectric device, and thus the flexure traveling wave can be generated in the resonator.
However, when the piezoelectric thin film has a grain boundary or a defect therein, an excellent piezoelectric characteristic cannot be obtained. In addition to this, a problem arises that the piezoelectric characteristic tends to deteriorate because of aging.
In addition, for the piezoelectric product before that is formed of the piezoelectric ceramic or the piezoelectric thin film, in order to provide a desired piezoelectric characteristic in the piezoelectric product, a polarization process step is required after the piezoelectric device is formed, the polarization process step in which direct current voltage is applied to the piezoelectric product to align the orientation of spontaneous polarization of the piezoelectric product. On this account, a problem arises that the fabrication process steps of the piezoelectric device are complicated as well as fabrication costs become high.
Patent Reference 1: JP-A-9-223824
Patent Reference 2: JP-A-2000-332568